Among conventional CNC lathes, there is a turret type CNC lathe having a tool turret indexing device operated by hydraulic cylinders for indexing the tool turret for changing and positioning the tool selected by a control unit. As most hydraulic cylinders applicable for a turret type CNC lathe are relatively bulky, hydraulic-operated tool turret indexing devices are generally built to the lathe manufacturer's own specification, and its operating speed is relatively slow; in most cases, it requires two seconds to complete one cycle of a tool changing operation.
There is another type of CNC lathe having a tool turret indexing device operated by solenoid units and magnetic brakes. In this order type of tool turret indexing device, a positioning pin (or pins) is employed in addition to the magnetic brakes to ensure the accuracy of indexing. But because of this, the device produces shocks and noises in each indexing operation. Furthermore, the positioning pin, which is inevitably subjected to constant shocks, tends to break easily and frequent repairs are necessary.
In order to eliminate the abovementioned problems with conventional tool turret indexing devices, a so-called roller-gear-cam-type tool turret indexing device employing a spiral-faced cam has been developed. This new tool turret indexing device contains a coupling device employing a first face gear fixedly mounted on an indexing shaft having one end formed into an indexing head on which tools are mounted, and a second face gear fixedly mounted on a stationary housing to be engaged with the first face gear. The indexing shaft is operated by a cam device driven by an input shaft to cause the indexing shaft to slide in one direction to cause the first face gear to disengage from the second face gear, and in an opposite direction to cause the first face gear to engage with the second face gear in a predetermined timing sequence. When the first face gear is disengaged from the second face gear, the indexing shaft is rotated by indexing rollers mounted on the indexing shaft. These indexing rollers are driven by a spiral-faced cam fixedly mounted on the same input shaft.
As shown in FIGS. 1, 2, and 3, the abovementioned roller-gear-cam type turret indexing device contains an input shaft 108A driven by a motor 108, a first cam 109 and a second cam 106 fixedly mounted on input shaft 108A and output shaft 119 having an indexing head 120 fixedly mounted on one end of output shaft 119, a thrust collar 114 fixedly mounted on output shaft 119, an indexing flange 115 integrally formed with output shaft 119, and a plurality of rollers mounted around the periphery of indexing flange 115.
A lever 110 is provided to be driven by first cam 109 to operate thrust collar 114 such that thrust collar 114 is caused to move in an axial direction while first cam 109 rotates.
A plurality of rollers 107 are driven by second cam 106 such that indexing flange 115 rotates a predetermined angle while second cam 106 rotates one complete rotation.
A coupling device containing a first-face gear 116A fixedly mounted on indexing head 120, and a second face gear 116B fixedly mounted on housing 101 which is provided to allow the rotation of output shaft 119 or lock output shaft 119 in place, with respect to housing 101.
In operation, output shaft 119 is moved axially forward to disengage first face gear 116A and second face gear 116B of the coupling device while first cam member 109 rotates to cause lever member 110 to operate and consequently the thrust collar 114 to move in a predetermined period sector of an indexing cycle.
As soon as first face gear 116A has been disengaged from second face gear 116B of the coupling device, the output shaft 119 is caused to rotate a predetermined angle as second cam member 106 rotates to cause rollers 107 and consequently, indexing disc 115 to rotate a predetermined angle equivalent to an indexing angle.
As soon as output shaft 119 has rotated the predetermined angle, first cam member 109 rotates to a position where thrust collar 124 is moved by lever member 110 to cause output shaft 119 to move axially back to its original position such that first face gear 116A is caused to engage with second face gear 116B of the coupling device to lock input shaft 108A in place onto housing 101 so as to complete the indexing cycle.
As described above, in the so-called roller-gear-cam-type turret indexing device, the indexing shaft is moved axially before and after the indexing head is rotated. Therefore, the movement of the relatively heavy output shaft tends to create a vibration.
Furthermore, in the above-mentioned "roller-gear-cam type" turret indexing device, the spiral-faced cam requires a highly precise finishing in order to assure an accurate indexing performance and such requirement tends to incur a high manufacturing cost. Moreover, the movement of the indexing head formed at one end of the indexing shaft tends to allow cutting chips to fall onto the surface of indexing shaft to hinder the indexing operation.
The turret indexing device of the present invention has effectively eliminated the above-mentioned problem with the conventional roller-gear-cam type turret indexing device.